PipeTransform docs unclear when dealing with multiple parameters

📚 Docs or angular.io bug report

Description

The PipeTransform’s transform parameters are unclear as it can now support multiple individual parameters or a rest param. It should be clarified how you can pass multiple parameters to the transform method. I suggest adding an additional example with multiple parameters as both of these ways of invoking the method are valid:

export class MyPipe implements PipeTransform { 
    // specify every argument individually   
    transform(value: any, arg1: any, arg2: any, arg3: any): any { }
    // or use a rest parameter
    transform(value: any, ...args: any[]): any { }
}

Example addition suggestion:

@Pipe({
    name: 'truncate'
})
export class TruncatePipe implements PipeTransform {

    transform(value: string, limit: number, trail: string): string {
        return value.substring(0, limit) + trail;
    }

}

Invoking {{ ‘Truncate me’ | truncate:8:‘!’ }} in a template produces Truncate!.

Additionally, it would be nice to document how to write a unit test for a pipe with multiple parameters. Similar to this:

it('should support multiple pipe parameters in the template', () => {
        @Component({
          template: `{{ text | truncate:8:'...' }}`,
        })
        class App {
          text = 'Truncate me';
        }

        TestBed.configureTestingModule({declarations: [App, TruncatePipe]});
        const fixture = TestBed.createComponent(App);
        fixture.detectChanges();

        expect(fixture.nativeElement.textContent).toEqual('Truncate...');
    });

What’s the affected URL?**

https://angular.io/api/core/PipeTransform

📷Screenshot

Can I open up a PR to make this change?

[Airblader]

But how multiple parameters are passed to a pipe from the template is clearly an Angular related question.

Definitely agreed.

[Airblader]

These are framework tests, so you want to make sure the pipe as a mechanism works end to end. When writing your own pipe you don’t need to test that the framework works, though.

Note that there certainly are pipes where a component unit test can be useful, just the majority of pipes in my experience wouldn’t need it.